Artificial leather



Patented Apr. 24, 1934 PATENT OFFICE ARTIFICIAL LEATHER Milton 0. Schur,Berlin, Company, Berlin, N. H.

N. H., assignor to Brown a corporation of Maine No Drawing. ApplicationJanuary 11 1932, Serial No. 586,091

4 Claims.

This invention relates to the manufacture of an artificial leather, andmore especially one which can be'produced at low cost and yet beserviceable as a shoe innersole stock, or for other purposes.

In making artificial leathers, one of the most inexpensive raw materialsavailable for making the fibrous foundation is preliberated cellulosepulp, and more specifically wood pulp which 'can be converted into awaterlaid web on machinery of the papermaking type. impregnated withrubber solutions of water-dispersed rubber, e. g., rubber latex, andthen dried, it takes on leather-like properties to such an extent thatit can serve for such purposes as'shoe innersoles. Thus, therubber-impregnated web is possessed of sufiicient residual porosity topermit breathing of the foot and its constituent fibers are sufiicientlybonded together to resist disintegration through the action of moistureand perspiration.

I have found that in making such artificial leathers, it is highlyadvantageous to use as the fibrous base a waterlaid web composed of ablend of both cellulose fibers like preliberated wood pulp and woolfibers. Aside from the fact that wool fibers lend themselves to webformation, especially when blended with cellulose fibers, and can take"on rubberfrom rubber solutions or aqueous dispersions, wool fibers canbe had on the market at a much lowercost than even wood pulps of thecheapest grade. For example, it is possible now to purchase woolcuttings or shoddies at as low as $10 a ton, which is much'lower thanthe current cost of even the cheapest grades of wood pulp. .These woolcuttings or shoddies are sometimes made up of wool fibers of differentcolors, in which case they impart a pleasing variegation of the web,both in its raw and rubber-impregnated state. The wool fibers alone,however, do not conduce to waterlaid Webs having a uniform texture,which result may, however, be had when ,cellulos'e fibers or the likeare blendedwith the wool fibers in aqueous suspension'and the mixedfibrous suspension is run off into a web on a suitable papermakingmachine, e. g., a machine of the Fourdrinier or cylinder type.

The cellulose fibers used as raw material may be any one or a mixture ofthe well-known chemical wood pulps, e. g., sulphite or kraft pulp,either in bleached or unbleached condition. Preferably, however, arefinedwood'pulp of an alpha cellulose content of about 93% to 96% isemployed, as such pulp leads to webs of greater absorptivity on a givenpapermaking machine.

When such a web is' Preliberated cellulose pulps other than wood pulpmay be used when available, in lieu of part or all of the wood pulp, forinstance the longer-fibered pulps derived from manila, sisal, ramie, orthe like. The blend may contain various proportions of preliberatedcellulose pulp and wool fiber, for instance a prepondera'nt proportionof either. on the other hand, the use of more cellulose pulp than woolfiber is ordinarily to bepreferred because of the uniform web textureattainable in such case without much trouble. For example, a blend ofabout to 50% refined wood pulp and about 25% to 50% Wool fiber has beenfound to yield an excellent web for use as an artificial leather base.

I shall now give a specific example of procedur which has been found togive an artificial leather eminently satisfactory for use as shoeinnersole stock. I first prepare an aqueous fiber suspension in a beaterengine made up of about 75% 75 refined wood pulp of an alpha cellulosecontent of about 93% to 96% and about 25% wool shoddy,. which maycontain fibers of mixed colors. The beater should be operated in such away as to eifect a mixing of the fibers without much hydration orgelatinization of the Wood pulp fraction, if a comparatively flexibleartificial leather is de- 1 sired; if a stifier leather is in view, theWood fibers may be correspondingly hydrated.

The mixed aqueous fiber suspension is diluted with sufiicient water toform a comparatively dilute and uniform fiber suspension,'which is runoff on a paper'making machine operated under conditions to deliver a dryweb havinga compactnessof, say, about 40 and a basis weight of about300. The compactness value is obtained by dividing the basis weight inpounds by the thickness in inches, and multiplying by the factor 10*. vThe expression basic weight as known in papermaking circles representsthe weight in pounds of 480 sheets whose dimensions are 24 x 36 inches,this being equivalent to 2880 square feet of sheet material. In otherwords, the compactness value really represents the weight of fiber perunit volume of sheet material.

The dried, raw web is then impregnated with a suitable latexcomposition, as by immersion in the composition, and then dried. Nodifliculty whatever-is encountered in securing complete impregnation ofthe sheet, because it is comparative-- 1y porous. Preferably, the latexcomposition contains casein as a stiflening agent, and also lime, whichlatter compound serves to prevent migration of the rubber particles tothe surface of the impregnated sheet during the drying operation, 110

It is desirable to add a slight amount of viscose a result ofimpregnation with a latex composito the latex composition, as theregenerated celtion and drying presents a moreperfect surface. luloseproduced in the sheet during drying im- This is evidently attributableto the resiliency of proves its characteristics. Wheh viscose is presthewool fibers and the tendency of a web con 5 ent in the composition,boric acid is also prefertaining such fibers to recover from anylocalized ably added along with the'viscose to promote the denting ormarring action which it undergoes regeneration of the cellulose from theviscose. during manufacturing operations. The fluffy The boric acid orits equivalent is added to the kind of webs of low compactness which Ifabriviscose without causing a gelling, and serves pricate as thefoundations for artificial leather prodmarily to neutralize part of thealkali associated nets are susceptible to becoming surface-blem with theviscose. A suitable anti-oxidant, such ished, especially when of highbasis weight.

as Agerite White is preferably added to the Thus, at a basis weight ofabout 150 pounds and latex composition in order to improve the ageinghigher, such webs tend to acquire surface cracks qualities of the dried,rubber-impregnated sheet. and other blemishes, probably on account oftheir I do not herein claim as the invention the advancontact with theinstrumentalities of the papertageous latex composition, as this subjectmatter making and impregnating machines, for instance is disclosed andclaimed in my patent application the rolls and/or drying drums of thesemachines, Serial No. 541,959, filed June 3, 1931. The parand/or probablybecause of the tendency of the ticular latex composition used as theimpregnant inner lay rs of a mp iv ly hi k sh t may have a total solidscontent (1. e., rubber and pipe or to crack when bent into a small arc.non-rubber solids) of about 9% in the bath A web made from only arefined wood pulp and whereinto the raw web is dipped. When the imhavinga basis weight of 200 pounds and a compregnated sheet is i d, it t i b t20% pactness of 40 showed surface defects even though to added solids,and compares favorably the smallest roll on the papermaking machine 25with an artificial leather made entirely of a reat the dry end d d texce 4 inches in fined wood pulp base and impregnated ith a, ameter.When the furnish contained 25% wool similar latex composition to a muchhigher solids fibers, there was no evidence whatever of surface content.I present herewith a table showing the defects in a web of the same highbas s Weight characteristics of the artificial leather of the and low cop Heretofore, in the manupresent invention, alongside of one whosefibrous facture of a 3-iron artificial leather (i. e., leather baseconsisted entirely of refined wood pulp of Of a thickness of 3/48inches) intended as fo a compactness of about 30 d hi h i bib dinnersoles, it was found necessary to use at least about twice as muchsolids from a common latex w pli f w b stock of a pa tn ss of aboutcomposition used as the impregnant: 40, in order to realize a product ofsatisfactory appearance. The plies were superposed and bonded togetherafter each had undergone impregnation with rubber independently toacquire the desired leather-like characteristics. If it is attempted toproduce a similar artificial leather product from only a single ply of300 pounds basis weight containing only cellulose fiber, it is foundthat the finished product is badly cracked on its surface and presents adistinctly inferior appearance. When, on the other hand, the furnishfrom which the web is prepared contains about 25% wool, it is found thata single-ply web can be properly fabricated at a basis weight of 300pounds or even higher, and that such a web can serve as the completebase for an artificial leather innersolepractically free from unsightlysurface markings. Besides, it is more economical to work with a singleply of heavy weight, because it is sufficiently strong asit comes 01fthe dry end of the paper machine, even at low compactnesses, say at acompactness of about 40, to resist rupture or breakage when processed asa continuous sheet and because the cost of laminating is eliminated.

It is noteworthy of mention that webs containing refined wood pulp of analpha cellulose content of, say, about 93% to 96% are generally moreabsorptive and lead to artificial leathers of greater flexibility andsuppleness than do unre-' fined pulps. If it is attempted to cheapen thefurnish by substituting unrefined pulp for part or all of the refinedwood pulp, the quality of the web is correspondingly impaired. It wasonly after considerable experimentation that wool fiber was establishedas being a component which would reduce the cost of the furnish and yetin Artificial (lgaagier 1 re fined wood pulp base) New artiflcialleather Solids added based on fiber) Thickness Stifiness, wide bend:

With direction of sheet Across direction of. sheet 45 Stiffness, sharpbend:

With direction of sheet Across direction of sheet Tack holding Internalply adhesion 50 It is thus seen that in so far as concerns thoseproperties such as stiffness, tack-holding ability, and internal plyadhesion, desired in innersoles, the new artificial leather comparesquite favorably with a much more expensive artificial leather 55containing only refined wood pulp as the fibrous base, and far moreadded solids. The new artificial leather has lower tear resistance thanthe single ply artificial leather used as a basis of com-. parison, butthis feature is not of great moment 0 in such articles as inner soles,which do not undergo tearing stresses in use. Were a two-ply artificialleather, but otherwise similar to the standard of comparison appearingin the table, used as a basis of comparison, however, the new 5artificial leather would measure up with such a two-ply artificialleather, even in such respects as tear resistance.

One of the important advantages attending the use of wool fiber alongwith cellulose fiber in the ""'70. -furnish-is that the web producibletherefrom is muctffreei ir m wrinkes, cracks, or other surcertainimportant respects enhance the quality face blemishes than we reparedfrom an allof the web and the ultimate artificial leather, cellulosefiber furnish, and acc gwrlixigLparticularly when the wool is used inproportion ber-imp t artificial leather produc up to, say, about 40% to50% of the dry weight 75 which the wool-containing web is converted asoftfieentirefller furnish. 150

,inches and multiplying by a a basis weight of fibers made up partly ofsubstantially unhytially unbeaten wood pulp h drated wood pulp andpartly of wool shoddy, said 'web having a compactness not exceedingabout 40, as determined by dividing its basis weight in pounds by itsthickness in inches and multiply-' ing by the factor 10-, and a basisweight'of at least about 150, but at the same time being substantiallyfree from surface defects.

3. A dried, latex-impregnated, waterlaid web of interfelted fibers madeup largely of substanaving an alpha celweight of at least time beingsubstantially free from surface delulose content of at least about 93%and a sub-1 ordinate proportion of wool shoddy, said'web having acompactness notexceeding'about 40, as determined by dividing its basisweight in pounds by its thickness in the factor 10-, and a about 150,but at the same tially free from surface defects.

:4. A dried, latex-impregn ted, of interfelted fibers 50% ofsubstantially unhydrated wood pulp of an alpha cellulose content ofabout 93% to 96% in admixture with about 25% .to 50% of wool shoddy,said web having a ceeding about 40, as determined by dividing its basisweight in pounds by its thickness in inches and multiplying by. thefactor 10-, and a basis about 150, but at the same basis weight of atleast waterlaid web fects. v

MILTON 0L SCHUR.

inches and multiplying by 7 made up of about 15% to time beingsubstancompactness not ex- 7

